Conventionally, lead acid batteries are used as an energy source for a wide variety of applications, including as a backup energy source for uninterruptible power supply (UPS) systems. Lead acid batteries have a long history due in part to their low cost. However, the usage of lead acid batteries also has its drawbacks, such as the poisonous nature of lead, their low energy density, risk of failure without notice, and their short lifecycles. Such problems have made lead acid batteries unsatisfactory for many applications, including UPS systems. As an alternative, lithium ion batteries have promise in replacing lead acid batteries for many applications. However, lithium ion batteries also are subject to difficulties in determining of the state of health (SOH) of the batteries and consequently the prevention of safety problems related to operation of the batteries, which have made lithium ion batteries undesirable in some applications, especially for large applications, such as a bulky UPS system (e.g. 800 kVA, 500V UPS system). Accordingly, lithium ion batteries are viable replacements for lead acid batteries in many of today's applications if safety concerns can be addressed and improved.